Preheating secondary air feeding furnace door mounted device



April 17, 1951 J F MCKEAGUE 2,549,219

PREHEATING SECONDARY AIR FEEDING FURNACE DOOR MOUNTED DEVICE Filed April 22, 1949 VENTOR Patented Apr. 17, 1951 PREHEATIN G SECONDARY AIR FEEDING FURNACE DOOR MOUNTED DEVICE John Francis McKeaguefThorold, Ontario, Canada Application April 22, 1949, Serial No. 89,096

2 Claims. I

My invention relates to improvements in combustion improving devices for furnaces, of the type which provides a supply of pre-heated air and distributes it to the best advantage over the fire bed of a furnace to ensure'complete combustion of the fuel gases.

An object of the invention is to provide such a device which may be readily installed in the door of a conventional domestic space heating furnace without altering other parts of the heating unit.

Another object is to devise a combustion aid which will be highly eflicient in its operation and will ensure complete combustion of the fuel gases generated in the furnace fire pot or fire bed by supplyingsecondary combustion air thereto, and which will, at the same time, efficiently preheat such secondary air to a temperature at which it will not cool off the unburned gases to which it supplies oxygen for combustion.

A still further object is to provide a combustion aid which will introduce secondary combustion air over the fire pot, but which does so under the control of the conventional draft controlling mechanism of the furnace, whereby the benefits of thermostatic or clock control of the otherwise conventional draft inlet may be maintained.

With the above and other objects, which will hereinafter appear as the specification proceeds. in view, my invention consists of the construction and arrangement all as hereinafter more particularly described and illustrated with reference to the accompanying drawing, in which:

Fig. 1 is a side elevational view, partially broken away, of a conventional domestic hot air furnace, showing my combustion improving device installed in the door thereof Fig. 2 is alongitudinal vertical sectional view of the combustion improving device proper on an enlarged scale;

Fig. 3 is an elevational view of the inner end of the device as shown in Fig. 2; and

Fig. 4 is an elevational view of the outer end of the device as shown in Fig. 2.

Like characters of reference designate correspending parts in the different views.

Referring to the drawing, my combustion improving device is adapted to be installed in the existing door I of any orthodox domestic heating furnace, suchas a hot air furnace indicated in general by reference character 2 of Fig. 1, although the door installation is purely a matter of convenience and the device may also be installed through the wall of the furnace if desired. The furnace 2 will have a fire pot or a fire bed indicated generally by reference character 3.

My combustion improving device proper consists of a tube 4 passing'through the furnace door I, provided with a cap 5 on its inner end and a bell mouth 6 on its outer end, and a damper l hinged, as at 8, on such mouth. Below the tube 4 on the furnace door is a chamber 9, substantially closed on all sides but one, the open side registering with the conventional secondary air inlet [0 of the furnace, which inlet may be pro- 'to such plate over an orifice l6 in the plate, to a make an integral unit which may be mounted in the door I of the furnace. enables the combustion improving device to take the form of a self-contained unit which may be attached to any existing furnace.

The inner end of the tube 4 comprising the cap 5 is provided with a plurality of nozzles ll, some of which are directed downwardly and. some laterally of the axis of the tube 4 to distribute air coming through the tube 4 over a wide area. Highly efiicient exchange of heat from the furnace fire between the outside of the tube 4 and air passing therethrough is effected by filling substantially the whole section of thetube with a bundle of pipes [8 of relatively small diameter and of good heat conducting material, and such pipes may be conveniently maintained in place by a section of wire mesh material 19 tack welded to the interior of the tube 4 at either end of the bundle of pipes. The chamber 9 is provided with downwardly and outwardly directed nozzles 20 for distributing heated air to the fire bed immediately below-the tube 4, and efficient heat exchange between the cold air coming through the chamber 9 and the outside of the chamber is effected by means of a pack 2| of layers of Wire screen filling the interior of the chamber.

The damper. l on the outer endof the bell mouth]; of the tube 4 may be opened or shut inlet of air to the tube 4, even when the damper is in the nominally closed position. Additional Such construction 3 adjustment of the amount of air admitted to the furnace through the tube 4 in the nominally closed position of the damper 7 may be provided by means of a rotatable plate 26 rotatable ona pin 2'], the plate 26 being provided with holes 28 and the damper I with holes 29 which register to a greater or lesser extent as the plate is rotated. A butterfly type damper 30 having an operating arm 3| enables the maximum amount of air drawn into the tube 4 to be set independently of the amount of opening of the damper 1.

In use, the combustion improving device is installed in the door l of a-furnace and the tube t is inserted into the furnace to a depth such that air drawn through the bell mouth 6 of the tube 4 is distributed evenly over the surface of the fire in the fire pot 3, so that the air drawn in through the tube 4 is thoroughly intermingled with the products of combustion from the fire bed, and the tube 4 is locked in such a position by inserting the pin I 3 into the nearest hole I4 in tube A. -With the furnace operating, and particularly when fuel has just been added to the furnace, secondary air, which would normally be admitted to the furnace through the damper I I, is drawn into the, furnace through the bell mouth 6 of the tube 4 and distributed evenly across the surface of the fire bed, and is'at the same time pre-heated to a substantially elevated temperature whereby any cooling effect on the fire bed is eliminated:

The pre-heating is effected by radiated heat from the fire bed heating upthe inner end of the tube 4, and thebundle of tubes l8, and due to the large area of the walls of such tubes [8, the rate of heat transferto the incoming air is very high and effective. Similarly, any air drawn in through the conventional shutter type damper ii is quickly and efiiciently heated by contact with the screen pack 2|.

, It is to be'understood, of course, that the shutter damper II and the nominally closed position of the damper T will be adjusted to admit just sufficient air to maintain emcient combustion ofthe fuel gases when the furnace is idling. When a new charge of fuel has been added to the furnace,

, the damper I will be opened to provide a large supplyof' pre-heated air to the surface of the fuel bed: Such damper I may be opened manually at the time the fuel is added, but preferably it is opened by pulling the chain 23 from the conventional chain draft control point remote from thev furnace, or even more preferably by a 'conventional power actuated draft mechanism controlled by athermostat. In any case, and particularly in the latter case, the'butterfiy damper 30 may be set at the proper angleby means of the lever 3! to pass the optimum amount of air,'regardboth under theidling condition and under the.

firing condition, representing, respectively, the minimum and maximum amounts of air, may be set by a relatively simple adjustment of the dampers 30 and l, without the necessity of making complicated adjustments to 1 the draft control mech anism operated through the chain 23. Small changes in the minimum draft adjustment which.

may be required for varying weather conditions Ill) can be simply and quickly made by use of the damper 26. I

' From the foregoing it should be obvious that I have provided a highly efficient device for preheating and injecting a supply of secondary air into a furnace, and that my preferred construction results in a substantially self -contained unit which may be installed in an existing furnace with a minimum of effort and with a minimum of alteration to the furnace. The chamber 9 with its highly efficient heat exchange medium in the form of the screen pack2l also supplies preheated air to the furnace even in the idling condition. By means of the two dampers 3D and l, the minimum and maximum operating air flows may be set precisely .to the amounts required for most efficient operation of the furnace, and these minimum and maximum adjustments can be made independently of the operating range of the draft control mechanism associated with the furnace. a

While I have illustrated and described a preferred embodiment of my invention, it is to be understood that such disclosure is for purposes of illustration only and it is intended to impose no limitations on the scope of the invention be tube for locking said draft tube in said mounting tube in any one of a plurality of extended positions, a bundle of tubes ofrelatively small diameter substantially filling the section of the draft tube which extends into the furnace, a damper on the outer end of said draft tube, and a plurality of draft dispersing nozzles on the inner end of said draft tube.

2. A combustion improving device as claimed in claim 1, wherein said damper comprises a plate passing through said plate adjacent its periph-.

hinged across the end of said draft tube, a screw cry, and a stopon the draft. tube engageablewith the inner end of said screw, for adjustably positioning the plate in a partially closed position.

- g JOHN FRANCIS "McKEAGUE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Feb. 18, 1936 

